Standards Update

   
 

Current Standards
International structured cabling standards are ratified by the International Standards Organisation (ISO), part of the United Nations.

Other worldwide recognized cabling organizations include the Electronic Industries Alliance (EIA) and the Telecommunications Industry Association (TIA).

Within the field of structured cabling, three standards are broadly comparable:


IA/TIA 568A (US), EN50173 (Europe) and ISO 11801 (International). The equivalent British Standard is BS EN 50173.
ISO 11801, Generic Cabling Standard sets out four classes of copper cabling installation to suit different applications:

Class A - is for voice telephony up to 100 KHz.

Class B - covers frequencies to 1MHz for voice and slow speed links to IBM 3270 terminals and similar.

Class C (Category 3) - represents frequencies to 16MHz and is suitable for most of the data applications in place prior to 1990.

Class D (Category 5) - was drafted in 1992, and finally ratified in 1995. Structured cabling systems conforming to Categories 3 and 4 still exist, however, Category 5 is the recognised standard for modern network applications. Category 5 installations are well established around the world, with approximately 95% of new and refurbishment structured cabling installations specifying Category 5 or above.

Category 5 - the current benchmark
For a cabling component or system to achieve Category 5 compliance it must meet all of the mechanical and electrical criteria covering; component design, system configuration and implementation procedure.

The two most important and internationally accepted standards documents are ISO 11801 and TIA 568A. Both are very similar.

Also, in the TIA document 568A, the link and channel are termed "Category 5", whereas in the ISO document only the components are referred to as "Category 5", with the link and channel termed "Class D".

Numerous tests are required to fully qualify a Category 5 or "Class D" link or channel. These verify the bandwidth, by measuring the quality of the signals transmitted and received, and includes all components within the structured cabling system.

To compare the test requirements for Category 5, with proposed and currently accepted performance standards which exceed Category 5, refer to the chart opposite. A glossary of terms explaining the differences between each test is included on pages 7 & 8.

Not all of the tests listed on page 2 are a requirement of the standard. Test equipment manufacturers have their own standards, which exceed the tests defined by ISO and TIA Category 5 documentation, providing more in-depth performance measurements.

"TIA TSB 67" covers the performance criteria for Level I and Level II testers, including the definition of a Basic Link. The link definition in ISO 11801 and TIA 568A are design definitions, while the Basic Link definition in TSB 67 is a test definition. The Basic Link includes the horizontal section of the cabling system which does not change, i.e. the horizontal cabling, patch panel and telecommunications outlet.

By the end of 1999, ISO 11801:95 will have an addendum to include the testing of patch cords. Until now, patch cords have not been tested. With the impending release of "Category 5 Enhanced", patch cord testing is now a requirement. Further tests to be conducted on the entire Link will include the testing for PowerSum which is necessary if Gigabit performance levels are to be achievable over copper cabling.

Beyond Category 5 - Category 5 Enhanced

There are currently three emerging standards: Category 5 Enhanced (5E), Category 6 and Category 7. Category 5 Enhanced (C5E), like Category 5 is a 100MHz classification. However, the performance requirements of a Category 5 Enhanced system are more stringent.

The purpose behind this standard is to provide an improved Attenuation to Crosstalk Ratio (ACR) and return loss, compared with conventional Category 5 solutions. This is partly achieved by reducing the NEXT levels in the cables and connecting hardware. Signal interference and corruption is therefore further reduced, improving signal integrity.

To ensure that this new standard will be supported by emerging technologies, additional testing criteria and equipment have been introduced.

The need to transmit increasing amounts of data has placed an additional strain on Category 5 cabling systems. To reduce data congestion, by increasing speed, certain emerging protocols utilise all 4 pairs of standard 4 pair cable, splitting the data equally on each pair. For example, in Gigabit Ethernet the data is split equally onto each of the 4 pairs.

This means that 250 Mbits of data are transmitted along each pair. Since more than one twisted pair can be transmitting at any one time, the total amount of interference on any one pair must be measured.

This type of measurement is called PowerSum, and it is applied to NEXT and ACR.

Category 6
Unlike earlier cabling standards, Category 6 or Class E is a 200MHz classification.

Initially only two parameters were proposed for Category 6. These were that any Category 6 solution must use the existing RJ45 plug and jack format, and that the channel PowerSum ACR (PSACR) must be positive at 200MHz. As the development of this standard has progressed, additional requirements have been drafted.

Requirements for NEXT, PSNEXT, ACR, PSACR, etc. are now beginning to emerge. Once again some new tests have been devised to further qualify the overall performance of the individual components and installed link or channel.

Two of these tests, Equal Level Far End Crosstalk (ELFEXT) and PowerSum Equal Level Far End Crosstalk (PSELFEXT) are necessary due to the latest high performance protocols transmitting data in both directions simultaneously.

The upper frequency of Category 6 testing is still under consideration. Some standards bodies quote 200MHz and others quote 250MHz. If the upper frequency is 250MHz then the limit for channel PowerSum ACR will be negative above 200MHz. This 25% increase in frequency is to ensure that the system does not fall apart just above 200MHz.

To achieve positive ACR up to 200MHz significant changes need to be made to the cabling system. To extend the frequency range of the system, either the attenuation or the crosstalk have to be reduced. When reducing attenuation, the cross-sectional area of the conductors must be increased, using more copper. This takes up more room and is much more expensive. The more cost efficient solution is to reduce NEXT.

Several cable manufacturers have already achieved better ACR through various means. Tighter twisting of the pairs or the provision of a spacer along the length of the cable have all been employed to reduce NEXT. Spacers and tighter twists are a suitable solution for cables, however, more complicated techniques are required when controlling these parameters in connecting hardware PCB.

High performance RJ45 jacks and very intricate PCB tracking is necessary to achieve the required levels of NEXT and other parameters.

Installation practices for Category 5 and 6 differ slightly, therefore additional care has to be taken to minimise any changes in the cable's performance, due to installation configuration or over-handling.

The differences in handing Category 6 products, links and channels, will require additional training, even for installers familiar with Category 5 installation practices.

The components with the most variable level of performance within Category 6 links and channels are the patch cords, fly leads and test cords. Slight variations in these components can have a massive effect on the overall performance of the system. Excelware has decided to test all

Category 6
patch cords for the foreseeable future to ensure their performance is adequate and stable enough to guarantee Category 6 link and channel performance.

Category 7
The useable bandwidth of a Category 7 solution is 600MHz + 25% (750MHz). This extreme bandwidth is outside the scope of conventional RJ45s and as such a new style of connector is required.
The absence of a definitive specification for this new connector is preventing the standard from advancing. There are other serious implications with regard to Category 7 solutions. In addition to the use of non-standard jacks, the entire installation must be shielded (Each cable consists of four individually foil shielded pairs with an overall braid shield). Unless the ground supply for the shielded system is clean and dedicated then all sorts of transmission aberrations may occur.
The future of Category 7 is assured, as it has been agreed that it will be included in the second revision of ISO 11801. However, Category 7 is most likely to succeed in countries where shielded solutions are most prevalent.
Currently, major UTP structured cabling markets such as the USA, UK and many others are not demanding Category 7 solutions, therefore prices will remain very high for the foreseeable future.
Fibre optic cabling to the desktop may become common place before Category 7 is fully integrated into copper structured cabling solutions.

   
 
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